Structure Formation in Supraparticles Composed of Spherical and Elongated Particles

Abstract

We studied the evaporation-induced formation of supraparticles from dispersions of elongated colloidal particles using experiments and computer simulations. Aqueous droplets containing a dispersion of ellipsoidal and spherical polystyrene particles were dried on superamphiphobic surfaces at different humidity values that led to varying evaporation rates. Supraparticles made from only ellipsoidal particles showed short-range lateral ordering at the supraparticle surface and random orientations in the interior regardless of the evaporation rate. Particle-based simulations corroborated the experimental observations in the evaporationlimited regime and showed an increase in the local nematic ordering as the diffusion-limited regime was reached. A thin shell of ellipsoids was observed at the surface when supraparticles were made from binary mixtures of ellipsoids and spheres. Image analysis revealed that the supraparticle porosity increased with an increasing aspect ratio of the ellipsoids.

Mesoscale simulations of diffusion and sedimentation in shape-anisotropic nanoparticle suspensions

“…We therefore restricted our simulations to ϕ ≤ 0.30, which corresponds to ϕ ex < 0.44 for our spherocylinders ( v ex / v = 1.45 and 1.41 for λ = 1 and 2), in order to focus our calculations on the isotropic phase. We confirmed this was the case by computing a global nematic order parameter, 93,94 finding it to be close to zero (0.02 and 0.03 for λ = 1 and 2 when ϕ = 0.30) as expected for an isotropic phase.…”

Nanocrystal Assemblies: Current Advances and Open Problems

“…Although the driving force behind structure formation remains incompletely understood, recent studies have established that hydrodynamic interactions play an important role in suppressing stratification. , The open questions include (i) the role of additives such as surfactants, (ii) the impact of surface-stimulated nucleation, and (iii) the effect of macroscopic flow fields within evaporating droplets and films . Another challenge comes with engineering supraparticles using anisotropic NCs, which can become arrested in sparsely packed disordered states, , including multicomponent cases. Such highly porous assemblies are characterized by large surface-to-volume ratios, making them promising materials for catalysis, as recently demonstrated for the enhanced photocatalytic activity of TiO 2 supraparticles …”